Peptides having amino acid sequences comparable to those found in peptidoglycans (PG) and PG-precursors (PG-PP) will be synthesized and used as antigens to detect anti-PG and/or anti-(PG-PP) in the sera of patients with Staphylococcus aureus - caused endocarditis and becteremia. Other peptides will be used as inhibitors of this antigen- antibody reaction to probe the antibody specificity. Still other peptides will be used as immunogens to determine the control of the immune response. The ability of some clinical isolates of S. aureus to synthesize in vitro a soluble PG (SPG) when grown in the presence of antibiotics will be determined and the results will be correlated with the anti-(PG-PP) titers found in the sera of the patients from which they were isolated. These SPG's will be purified by affinity chromatography (purified rabbit anti-(PG-PP) or vancomycin) and the physical, chemical and biological properties of these SPG's will be determined. The mechanisms of enzymes engaged in PG biosynthesis, such as the soluble exocellular DD-carboxypeptidase-transpeptidase of Streptomyces R61 will be probed by synthetic peptide substrates, inhibitors and affinity labeling reagents in an effort to ascertain whether penicillin binds as a D-Ala-D-Ala analogue.